1. Field of Invention
This invention relates to a fuel injection nozzle for a diesel engine. This nozzle generally comprises a nozzle body having a spray tip with the discharge orifices and an axially movable fuel control valve within the nozzle body.
2. Description of Prior Art
In the diesel engine the fuel is injected under high pressure into the combustion chamber with a high temperature air charge. To insure a good mixing of the fuel with the air, the injection is carried out by single or multi-holed nozzles. These nozzles were disclosed by the U.S. Pat. Nos. 4,106,702; 4,139,158 and 4,200,237. The essential diesel engine's operational characteristics, such as fuel consumption, thermal and mechanical loads, smoke and exhaust emissions, are decisively influenced by the fuel-air mixing during the combustion process. Fuel-air mixing is affected by a range of design and operating variables which include fuel injection velocity, the geometry of the combustion chamber, the air charge motion and the nozzle configuration. One of the important characteristics of the fuel nozzle is spray formation or control of the physical characteristics of the spray so as to secure proper mixing of fuel and air both in time and space.
It is known that the fuel jet produced by a conventional hole type fuel injection nozzle consists of the very compact center portion of the spray, or the core, and the peripheral portion. This nozzle usually provides good atomization only in the peripheral portion of the fuel jet, giving a relatively fuel-rich mixture in the core. Consequently, during combustion, the peripheral portion of the spray is quickly evaporized in a high temperature gas; however, the evaporation of the core is slower and thus is the major cause of the smoke formation and inefficient engine operation.
Another problem in the current hole type nozzle is associated with the discharge orifices. Experience has shown that the size of the nozzle discharge orifices has a marked effect on the degree of atomization. The smaller the discharge orifice, the better atomization and faster fuel-air mixing. On the other hand, the smaller the orifice, the higher the probability that it will be plugged by carbon deposits or impurities in the fuel.